U.S. President Barack Obama said the withdrawal of American combat forces from all Iraqi cities on Tuesday is "an important milestone." Mr. Obama said he expects more violence in Iraq, but that the country will emerge stable and sovereign.

President Obama said more work needs to be done in Iraq, but that important progress has been made.

"The Iraqi people are rightly treating this day as a cause for celebration. This is an important step forward, as a sovereign and united Iraq continues to take control of its own destiny," he said.

At a White House event saluting service organizations, the president said with Iraq's progress comes responsibility.

"Iraq's future is in the hands of its own people, and Iraq's leaders must now make some hard choices necessary to resolve key political questions, to advance opportunity and to provide security for their towns and their cities," he added.

Mr. Obama pledged that the United States will be "a strong partner to the Iraqi people."

The president noted what he called the "senseless bombing" in a crowded market in the northern city of Kirkuk on Tuesday, and he predicted "difficult days ahead." But Mr. Obama said he is confident that the forces of destruction will fail.

"The future belongs to those who build, not those who destroy. And today's transition is further proof that those who have tried to pull Iraq into the abyss of disunion and civil war are on the wrong side of history," the president said.

The Obama administration's strategy is to remove all U.S. combat brigades from Iraq by September of next year, and to remove all U.S. troops from the country by the end of 2011.

Earlier, White House Press Secretary Robert Gibbs said U.S. commanders in Iraq are confident that Iraqi security forces will be able to take control of the nation's cities.

Gibbs also said that Vice President Joe Biden will lead the administration's Iraq policy and work with the Iraqis to help them bridge their political differences.